Process for improving the adhesion of polymeric materials to metal surfaces

ABSTRACT

A process is described which is useful in treating metal surfaces to increase the adhesion of polymeric materials thereto. The process involves treating the metal surface with a pre-dip which comprises an aqueous solution with pH of from 5 to 12 and then further treating the metal surface with an adhesion-promoting composition comprising an acid, an oxidizer and a corrosion inhibitor.

BACKGROUND OF THE INVENTION

It has long been known that the strength of the adhesive bond formedbetween the copper metal of the circuitry innerlayers and the curedpre-preg layers, or other non-conductive coatings, in contact therewithleaves something to be desired, with the result that the curedmultilayer composite or the coating is susceptible to delamination insubsequent processing and/or use. In response to this problem, the artdeveloped the technique of forming on the copper surfaces of thecircuitry innerlayers (before assembling them with pre-preg layers intoa multilayer composite) a layer of copper oxide, such as by chemicaloxidation of the copper surfaces. The earliest efforts in this regard(so-called “black oxide” adhesion promoters) produced somewhat minimalimprovement in the bonding of the circuitry innerlayers to thedielectric substrate layers in the final multilayer circuit, as comparedto that obtained without copper oxide provision. Subsequent variationson the black oxide technique included methods wherein there is firstproduced a black oxide coating on the copper surface, followed bypost-treatment of the black oxide deposit with 15% sulfuric acid toproduce a “red oxide” to serve as the adhesion promoter, such asdisclosed by A. G. Osborne, “An Alternate Route To Red Oxide For InnerLayers”, PC Fab. August 1984, as well as variations involving directformation of red oxide adhesion promoter, with varying degrees ofsuccess being obtained. The most notable improvement in this art isrepresented in the U.S. Pat. Nos. 4,409,037 and 4,844,981 to Landau, theteachings both of which are included herein by reference in theirentirety, involving oxides formed from relatively highchlorite/relatively low caustic copper oxidizing compositions, andproducing substantially improved results in circuitry innerlayeradhesion.

As earlier noted, the assembled and cured multilayer circuit compositeis provided with through-holes which then require metallization in orderto serve as a means for conductive interconnection of the circuitrylayers of the circuit. The metallizing of the through-holes involvessteps of resin desmearing of the hole surfaces, catalytic activation,electroless copper depositing, electrolytic copper depositing, and thelike. Many of these process steps involve the use of media, such asacids, which are capable of dissolving the copper oxide adhesionpromoter coating on the circuitry innerlayer portions exposed at or nearthe through hole. This localized dissolution of the copper oxide, whichis evidenced by formation around the through-hole of a pink ring or halo(owing to the pink color of the underlying copper metal therebyexposed), can in turn lead to localized delamination in the multilayercircuit.

The art is well aware of this “pink ring” phenomenon, and has expendedextensive effort in seeking to arrive at a multilayer printed circuitfabrication process which is not susceptible to such localizeddelamination. One suggested approach has been to provide the adhesionpromoting copper oxide as a thick coating so as to retard itsdissolution in subsequent processing simply by virtue of sheer volume ofcopper oxide present. This turns out to be essentiallycounter-productive, however, because the thicker oxide coating isinherently less effective as an adhesion promoter per se. Othersuggestions relating to optimization of the pressing/curing conditionsfor assembling the multilayer composite have met with only limitedsuccess.

Other approaches to this problem involve post-treatment of the copperoxide adhesion promoter coating prior to assembly of circuitryinnerlayers and pre-preg layers into a multilayer composite. Forexample, U.S. Pat. No. 4,775,444 to Cordani discloses a process in whichthe copper surfaces of the circuitry innerlayers are first provided witha copper oxide coating and then contacted with an aqueous chromic acidsolution before the circuitry innerlayers are incorporated into themultilayer assembly. The treatment serves to stabilize and/or protectthe copper oxide coating from dissolution in the acidic mediaencountered in subsequent processing steps (e.g. through-holemetallization), thereby minimizing pink ring/delamination possibilities.

U.S. Pat. No. 4,642,161 to Akahoshi et al, U.S. Pat. No. 4,902,551 toNakaso et al, and U.S. Pat. No. 4,981,560 to Kajihara et al, and anumber of references cited therein, relate to processes in which thecopper surfaces of the circuitry innerlayers, prior to incorporation ofthe circuitry innerlayers into a multilayer circuit assembly, are firsttreated to provide a surface coating of adhesion-promoting copper oxide.The copper oxide so formed is then reduced to metallic copper usingparticular reducing agents and conditions. As a consequence, themultilayer assembly employing such circuitry innerlayers will notevidence pink ring formation since there is no copper oxide present forlocalized dissolution, and localized exposure of underlying copper, insubsequent through-hole processing. As with other techniques, however,processes of this type are suspect in terms of the adhesion attainablebetween the dielectric substrate layers and the metallic coppercircuitry innerlayers. This is particularly so in these reductionprocesses since the circuitry bonding surface not only is metalliccopper, but also presents the metallic copper in distinct phases (i.e.,(1) copper-from-reduction-of-copper oxide over (2) copper of the copperfoil) which are prone to separation/delamination along the phaseboundary.

U.S. Pat. Nos. 4,997,722 and 4,997,516 to Adler similarly involveformation of a copper oxide coating on the copper surfaces of circuitryinnerlayers, followed by treatment with a specialized reducing solutionto reduce the copper oxide to metallic copper. Certain portions of thecopper oxide apparently may not be reduced all the way to metalliccopper (being reduced instead to hydrous cuprous oxide or cuproushydroxide), and those species are thereafter dissolved away in anon-oxidizing acid which does not attack or dissolve the portionsalready reduced to metallic copper. As such, the multi-layer assemblyemploying such circuitry innerlayers will not evidence pink ringformation since there is no copper oxide present for localizeddissolution, and localized exposure of underlying copper, in subsequentthrough-hole processing. Here again, however, problems can arise interms of the adhesion between the dielectric layers and metallic coppercircuitry innerlayers, firstly because the bonding surface is metalliccopper, and secondly because the metallic copper predominately ispresent in distinct phases (i.e., (1) copper-from-reduction-of-copperoxide over (2) copper of the copper foil), a situation prone toseparation/delamination along the phase boundary.

U.S. Pat. No. 5,289,630 to Ferrier et al., the teachings of which areincorporated herein by reference in their entirety, reveals a processwhereby an adhesion promoting layer of copper oxide is formed on thecircuit elements followed by a controlled dissolution and removal of asubstantial amount of the copper oxide in a manner which does notadversely affect the topography.

PCT Application No. WO 96/19097 to McGrath (and related U.S. Pat. No.5,800,859), the teachings of which are incorporated by reference hereinin their entirety, discusses a process for improving the adhesion ofpolymeric materials to a metal surface. The process discussed involvescontacting the metal surface with an adhesion-promoting compositioncomprising hydrogen peroxide, an inorganic acid, a corrosion-inhibitorand a quaternary ammonium surfactant.

U.S. Pat. No. 5,869,130 issued to Ferrier teaches a process forincreasing the adhesion of a polymeric material to a metal surfacecomprising contacting the metal surface with an adhesion-promotingcomposition comprising an oxidizer, an acid, a corrosion inhibitor and asource of halide ions. U.S. Pat. No. 6,020,029 issued to Ferrier, etal., teaches a process for increasing the adhesion of a polymericmaterial to a metal surface comprising contacting the metal surface withan adhesion-promoting composition comprising an oxidizer, an acid and acorrosion inhibitor, followed by contacting the metal surface with analkaline solution.

With processes such as those disclosed by U.S. Pat. Nos. 5,800,859,5,869,130 and 6,020,029, it has been found advantageous to use a pre-dipdirectly prior to treatment of the metal surface with theadhesion-promoting composition. The use of a pre-dip can increase theuniformity of the conversion coating achieved in the adhesion-promotingcomposition. If a pre-dip is used, the pre-dip may generally consist ofthe same essential composition as the adhesion-promoting compositionexcept at lower concentrations and is used at room temperature. As such,pre-dips currently used in the art of the foregoing processes have beencomposed of a corrosion inhibitor and hydrogen peroxide in an acidmatrix with pH below about 2.

While the foregoing pre-dips have been useful in increasing theuniformity of the conversion coating created by the adhesion-promotingcomposition, they have some drawbacks. Specifically, the acid oxidizingnature of the foregoing pre-dips readily dissolves the metal surfacethereby reducing the life of the pre-dip and creating metal bearingwaste solutions which can be difficult to dispose of. In addition,unnecessary dissolution of the metal surface is undesirable from thepoint of view of the design of the article being treated, particularlyprinted circuits.

It has now been discovered that pre-dips not based upon the compositionof the adhesion-promoting solution, specifically not containing hydrogenperoxide and of only slightly acid to alkaline in pH, can increase theuniformity of the conversion coating created in the adhesion promotingcomposition to a greater extent than pre-dips previously used while notsubstantially dissolving the metal surface and providing a longerworking life than previously known pre-dips. Specifically it hasdiscovered that pre-dips containing no hydrogen peroxide are useful inincreasing the uniformity of the subsequent conversion coating.

This invention proposes a process for improving the adhesion ofpolymeric materials to a metal surface, especially copper or copperalloy surfaces. The process proposed herein is particularly useful inthe production of multilayer printed circuits. The process proposedherein provides optimum adhesion between the metallic and polymericsurfaces (i.e. the circuitry and the intermediate insulating layer),eliminates or minimizes pink ring and operates economically, all ascompared to conventional processes.

SUMMARY OF THE INVENTION

The inventors herein propose a process for improving the adhesion ofpolymeric materials to metal surfaces, particularly copper and copperalloy surfaces. The proposed process comprises:

1). Contacting the metal surface with a slightly acid to neutral oralkaline (preferably pH 5-12, most preferably pH 7-12) pre dip and thendirectly contacting the metal surface with an adhesion-promotingcomposition comprising:

a) an oxidizer;

b) an acid;

c) a corrosion inhibitor;

2) thereafter bonding the polymeric material to the metal surface.

The inventor has found that the foregoing process improves the adhesionof metal surfaces to the polymeric materials, particularly when themetal surfaces comprise copper or copper alloys. The process proposed isparticularly suited to the production of multilayer printed circuitboards.

DETAILED DESCRIPTION OF THE INVENTION

The inventor herein has found that the adhesion between a metal surfaceand a polymeric material is enhanced by contacting the metal surfacewith an adhesion-promoting composition prior to bonding the polymericmaterial to the metal surface. The invention therefore proposes aprocess for increasing the adhesion of a polymeric material to a metalsurface, said process comprising:

1) contacting the metal surface with a neutral or alkaline (preferablypH 5-12, most preferably pH 7-12) pre dip and then directly contactingthe metal surface with an adhesion-promoting composition comprising:

a) an oxidizer;

b) an acid;

c) a corrosion inhibitor;

d) optionally, an organic nitro compound, preferably an aromatic nitrocompound, and most preferably an organic nitro compound selected fromthe group consisting of sodium meta-nitrobenzenesulfonate,para-nitrophenol, 3,5-dinitrosalicylic acid and 3,5-dinitrobenzoic acid.

e) optionally, a benzotriazole with an electron withdrawing group in the1-position which electron withdrawing group is a stronger electronwithdrawer than a hydrogen group and which electron withdrawing group ispreferably selected from the group consisting of hydroxy groups, aminogroups, nitro groups, nitrile groups, sulfonate groups, carboxylategroups, halide groups, mercaptan groups, and unsaturated alkyl groups;

f) optionally, adhesion enhancing species, which species are selectedfrom the group consisting of molybdates, tungstates, tantalates,niobates, vanadates, isopoly or heteropoly acids of molybdenum,tungsten, tantalum, niobium, vanadium, and combinations of any of theforegoing;

g) optionally, a water soluble polymer; and

h) optionally, a source of halide ions.

2) thereafter bonding the polymeric material to the metal surface.

The inventor has found that the proposed adhesion-promoting compositionproduces a micro-roughened conversion-coated surface upon the metal. Thesurface produced is particularly suited to bonding with polymericmaterials in that significantly increased adhesion values are achievedas compared to a non-treated metal surface. In addition the conversioncoated (treated) metal surface maintains the increased adhesion overtime and decreases the likelihood of any unwanted reactions occurringover time between the metal and the polymeric material.

The process proposed is particularly suited to the manufacture ofmultilayer printed circuit boards. Thus, in this application, the metalcircuitry (usually copper) of the innerlayers is treated with theadhesion-promoting composition proposed herein. After treatment,followed by water rinsing, the innerlayers are bonded together withpolymeric materials such as pre-pregs or imageable dielectrics,resulting in the multilayer printed circuit board.

The metal surface to be treated may comprise a variety of metals such ascopper, copper alloys, nickel and iron. However, the process of theinvention produces the best results when the metal surfaces comprisecopper or copper alloys. The polymeric material may be a variety ofpolymeric materials including pre-preg materials, imageable dielectrics,photoimageable resins, soldermasks, adhesives or polymeric etch resists.

It has been discovered that contacting the metal surface to be treatedin the adhesion-promoting composition with a pre-dip solution directlyprior contact with the adhesion-promoting composition can increase theuniformity of the conversion coating formed. The inventor has discoveredthat the use of a pre-dip with a pH in the range of 5 to 12, preferablyin the range of 7 to 12 and most preferably in the range of 7 to 10 ismost beneficial in improving the uniformity of the conversion coating.The pre-dip may comprise an aqueous solution of a corrosion inhibitor(s)with the pH adjusted into the foregoing ranges, preferably the corrosioninhibitor(s) is the same or similar to those used in theadhesion-promoting composition. If used, the concentration of corrosioninhibitor in the pre-dip may range from 0.1 to 50 grams per literpreferably from 0.2 to 5 grams per liter. In the alternative, or inaddition thereto, the pre-dip may comprise an aqueous solution adjustedsuch that the pH is within the foregoing recommended ranges and in thatcase the pre-dip preferably also comprises a buffer, such as trisodiumphosphate, sodium bicarbonate, sodium carbonate, borax, or mixtures ofthe foregoing. Potassium carbonate, potassium bicarbonate andtripotassium phosphate are also useful. If used, the concentration ofbuffer in pre-dip may range from 0.1 to 50 grams per liter but ispreferably from 0.5 to 10 grams per liter. In all cases, the pH of thepre-dip may be adjusted such that it falls within the foregoing givenranges of pH with acids or bases such as sulfuric acid or sodiumhydroxide. Preferably, as previously noted, the pre-dip does not containhydrogen peroxide, persulfates or similar oxidizers. The metal surfacesto be treated are preferably contacted with the pre-dip at roomtemperature for from 30 seconds to 5 minutes, preferably from 1 to 2minutes. The metal surfaces are then contacted with theadhesion-promoting composition, preferably without any rinsing inbetween.

The oxidizer used in the adhesion-promoting composition may comprise anyoxidizer which is capable of oxidizing the metal surface in the matrixof the adhesion-promoting composition. The inventors have found hydrogenperoxide and persulfates to be particularly preferred oxidizers for usein the process of the invention, with hydrogen peroxide being the mostpreferred oxidizer. The concentration of the oxidizer in theadhesion-promoting composition may range from 0.5 to 120 grams per literbut is preferably from 2 to 60 grams per liter and is most preferablyfrom 3 to 30 grams per liter.

The acid utilized in the adhesion-promoting composition may be any acidwhich is stable in the matrix, however, the inventors have found mineralacids to be particularly preferred.

Sulfuric acid is especially preferred. The concentration of the acid inthe adhesion-promoting composition may range from 1 to 360 grams perliter but is preferably from 20 to 110 grams per liter.

The corrosion inhibitor used in the adhesion-promoting composition is acompound which effectively reacts with the metal surface to form aprotective complex layer. Preferred corrosion inhibitors are selectedfrom the group consisting of triazoles, benzotriazoles, tetrazoles,imidazoles, benzimidazoles and mixtures of the foregoing. Benzotriazolesare particularly preferred. The concentration of the corrosion inhibitorin the adhesion-promoting composition may range from 0.1 to 50 grams perliter but is preferably from 0.2 to 5 grams per liter.

The inventors have found that the inclusion of organic nitro compounds,preferably aromatic nitro compounds, in the adhesion promotingcomposition yields a composition which will react with a metallicsurface, particularly copper or copper alloys, to give a uniformconversion coated metallic surface which bonds well to polymericmaterials, while etching the metal surface at relatively low rates. Lowmetal etch rates are advantageous for at least three reasons. First, alow etch rate removes less metal from the surface thereby leaving moreof the original metal cross section in tact. The foregoing isparticularly important for circuit traces with impedance or resistancetolerances which must be maintained since these properties are directlyrelated to the cross sectional area of the circuit. Second, low metaletch rates allow the opportunity for reworking defective parts. Lastly,low metal etch rates reduce the rate at which metal builds up in theadhesion promoting composition. Since metal build up in the adhesionpromoting composition has an effect upon the ultimate useable life ofthe composition, lower etch rates lead to an extended useable life forthe adhesion promoting solutions in terms of the maximum square feet ofmetal processable per gallon of adhesion promoting composition. Theorganic nitro compounds useable in the adhesion promoting composition ofthis invention are preferably aromatic nitro compounds. Some examples ofparticularly useful organic nitro compounds are sodiummeta-nitrobenzenesulfonate, para-nitrophenol, 3,5-dinitrosalicylic acid,and 3,5-dinitrobenzoic acid. The concentration of the organic nitrocompound in the adhesion promoting composition may range from 0.05 to 25grams per liter, but is preferably from 0.1 to 10 grams per liter and ismost preferably from 0.2 to 2 grams per liter.

The inventors have also found that the addition of a benzotriazole withan electron withdrawing group in the 1-position, which electronwithdrawing group is a stronger electron withdrawer than a hydrogengroup, produces advantages with respect to the uniformity of the coatingproduced and the adhesion achieved after bonding. The inventors havefound that the electron withdrawing group is preferably selected fromthe group consisting of hydroxy groups, amino groups, nitro groups,nitrile groups, sulfonate groups, carboxylate groups, halide groups,mercaptan groups and unsaturated alkyl groups. Most preferably theelectron withdrawing group is a hydroxy group and thus the mostpreferable material in this regard is 1-hydroxy benzotriazole with thefollowing structure:

The corrosion inhibitor and the benzotriazole with an electronwithdrawing group in the 1-position may both be the same compound. Forinstance, 1-hydroxybenzotriazole may fill the roles of both thecorrosion inhibitor and the benzotriazole with the electron withdrawinggroup in the 1-position.

The advantages achievable with the use of the foregoing materials in theadhesion-promoting composition are most pronounced when a source ofadhesion enhancing species, as described below, is used in conjunctionwith the foregoing materials in the adhesion-promoting composition. Theinventors have found that the combination proposed produces synergisticeffects. The concentration of the benzotriazole with the electronwithdrawing group in the 1-position can range from 0.2 g/l to 20 g/l butis preferably from 0.5 g/l to 5 g/l.

The source of adhesion enhancing species can be any material, which willsupply species selected from the group consisting of molybdates,tungstates, tantalates, niobates, vanadates and mixtures thereof to theadhesion promoting composition. Such sources include alkali metal saltsof molybdates, tungstate, tantalates, niobates, vanadates and mixturesthereof such as sodium (or potassium) molybdate, tungstate, niobate orvanadate, and heteropoly acids or isopoly acids of molybdenum, tungsten,tantalum, niobium or vanadium. Thus, molybdates or tungstates whichinclude heteroatoms such as phosphorous, silicon, cobalt, manganese andtungsten are suitable. Preferred sources include iso and heteropolyacids of molybdenum, tungsten, niobium, vanadium and mixturesthereof such as molybdic acid, vanadic acid and tungstic acid. The mostpreferred source of adhesion enhancing species is molybdic acid. Theconcentration of adhesion enhancing species in the adhesion promotingcomposition may range from 1 mg/l to 500 mg/l (based on the adhesionenhancing ion content) but is preferably from 5 mg/l to 200 mg/l. Theadhesion-enhancing species may be utilized with or without thebenzotriazole with the electron withdrawing group in the 1-position.

Optionally, the adhesion-promoting composition may also comprise a watersoluble polymer. If used, the water soluble polymer is preferably not awetter or surfactant but is instead a water soluble homopolymer orcopolymer of low molecular weight water soluble monomers. Mostpreferably, the water soluble polymer is a polymer of ethylene oxide, anethylene oxide-propylene oxide copolymer, polyethylene glycols,polypropylene glycols or polyvinyl alcohols. Among the most preferredare the polymers of ethylene oxide, or polyethylene glycols sold by theUnion Carbide Company under the tradename Carbowax. The inventors havefound Carbowax 750 and Carbowax MPEG 2000 to be particularly useful.Also particularly useful are the ethylene oxide polymers or ethyleneoxide-propylene oxide copolymers sold by the BASF or Company under thePluronic tradename. The concentration of the water soluble polymer inthe adhesion-promoting composition can range from 0.2 to 15 grams perliter, but is preferably from 3 to 6 grams per liter.

The adhesion promoting composition preferably contains a source ofhalide ions. The source of halide ions may be any compound which wouldprovide halide ions in the matrix of the adhesion-promoting composition.Preferably, the source of halide ions are alkaline metal salts such assodium chloride or potassium chloride, oxohalides such as sodiumchlorate or potassium chlorate, or halide bearing mineral acids such ashydrochloric acid. Preferably the source of halide ions provideschloride ions to the adhesion-promoting composition. The concentrationof the source of halide ions in the adhesion-promoting composition mayrange from 0.5 to 500 milligrams per liter but is preferably from 1 to12 milligrams per liter, all based on halide ion content.

Thus, the adhesion-promoting composition should contain an acid, anoxidizer, a corrosion inhibitor and an organic nitro compound.Preferably the composition also comprises a benzotriazole with anelectron withdrawing group in the 1-position as described herein or thecorrosion inhibitor may be the benzotriazole with the electronwithdrawing group in the 1-position. In either case, the compositionpreferably also comprises adhesion enhancing species as describedherein, whether or not the benzotriazole with the electron withdrawinggroup in the 1-position is used or not. In addition, the adhesionpromoting composition also preferably comprises a source of halide ions.

The metal surface can be treated with the adhesion-promoting compositionin a variety of ways, including immersion, spray, or flood. Thetemperature of the adhesion-promoting composition during treatment mayrange from 80° F to 150° F. but is preferably from 90° F. to 120° F. Thetreatment time will vary depending upon the temperature and method oftreatment but may range from 15 seconds to 15 minutes and is preferablyfrom 1 to 2 minutes.

The following examples are illustrative of the invention but should notbe taken as limiting:

The following cycle was used in processing the copper clad panels andcopper foils in all of the following examples:

Time (Min) 5% Sulfuric acid, 70° F. 1 Cold Water Rinse 1 Alkaline SoakCleaner 160° F. 2 Cold Water Rinse 2 Pre-dip as noted in Table I, 70° F.1 Adhesion Promotion Solution, 100° F. 1 Cold Water Rinse 1 Forced AirDry 1

The adhesion-promoting solution used in each of the following examplesconsisted of MultiBond 100 available from MacDermid, Incorporated, 245Freight Street, Waterbury, Conn. 06702 and was prepared in accordancewith the published instructions. The pre-dip used was formulated foreach numbered example as indicated in the following Table I.

TABLE I Example No. Pre-Dip Composition 1 No Pre-dip 2 2 g/lbenzotriazole, 2% v/v of 50% hydrogen peroxide, pH 2.0 with sulfuricacid 3 2 g/l benzotriazole in sulfuric acid with sodium carbonate to pH7.3 4 2 g/l benzotriazole in sulfuric acid with sodium hydroxide to pH8.0 5 2 g/l benzotriazole in sulfuric acid with borax decahydrate to pH7.3 6 2 g/l benzotriazole in sulfuric acid with trisodium phosphate topH 7.3 7 Pre-dip No. 4 with pH raised to 10.6 with sodium hydroxide 8 2g/l benzotriazole in dilute sulfuric acid with 5 g/l sodium carbonatewith pH raised to 12.0 with sodium hydroxide. 9 2 g/l benzotriazolesulfuric acid with 2 g/l sodium phosphate and pH raised to 5.5 withtrisodium phosphate. 10 5 g/l sodium bicarbonate, pH 8.5 11 5 g/l boraxdecahydrate, pH 9.5 12 5 g/l sodium bicarbonate with pH lowered to 6.5with sulfuric acid.

Each of the foregoing pre-dips was used with the notedadhesion-promotion solution to process copper clad panels and copperfoils. The appearance of the treated copper surfaces is noted in TableII. After treatment, the copper clad panels and foils were laminatedtogether with Nelco 4205-2 B-Stage material and etched to form one-inchstrips. The strips were then peeled to determine the strength of thecopper to polymer bond after lamination. The results obtained arereported in Table II:

TABLE II Pre-dip Appearance Peel/Strength, lb./in 1 Very nonuniform pinkand purple/pink 6.0 2 Uniform purple/pink 5.8 3 Uniform purple/pink 6.04 Uniform purple/pink 6.0 5 Uniform purple/pink 6.0 6 Uniformpurple/pink 6.2 7 Uniform purple/pink 6.0 8 Uniform purple/pink 5.8 9Uniform purple/pink 5.5 10 Uniform purple/pink 5.8 11 Slightlynonuniform purple/pink 6.0 12 Slightly nonuniform purple/pink 5.8

What is claimed is:
 1. A process for increasing the adhesion of apolymeric material to a metal surface, said process comprising: a.contacting said metal surface with a pre-dip, said pre-dip comprising anaqueous solution of a buffer and with a pH from 5 to 12; thereafter b.contacting the metal surface with an adhesion-promoting compositioncomprising:
 1. an oxidizer;
 2. an acid; and
 3. a corrosion inhibitor;and thereafter c. bonding the polymeric material to the metal surface;wherein said metal surface is contacted with the adhesion-promotingcomposition directly after contact with the pre-dip and without anyintervening process or rinse steps.
 2. A process according to claim 1,wherein the pre-dip comprises an aqueous solution with a pH from 7 to12.
 3. A process according to claim 1, wherein the pre-dip alsocomprises a corrosion inhibitor.
 4. A process according to claim 1,wherein the adhesion-promoting composition also comprises at least onematerial selected from the group consisting of organic nitro compounds,a benzotriazole with an electron withdrawing group in the 1-positionwhich electron withdrawing group is a stronger electron withdrawer thana hydrogen group, water soluble polymer, and a source of halide ions. 5.A process according to claim 1, wherein the adhesion-promotingcomposition also comprises adhesion enhancing species, which species areselected from the group consisting of molybdates, tungstates,tantalates, niobates, vanadates, isopoly or heteropoly acids ofmolybdenum, tungsten, tantalum, niobium, vanadium and combinations ofany of the foregoing.
 6. A process according to claim 1, wherein thepre-dip comprises a buffer selected from the group consisting oftrisodium phosphate, sodium bicarbonate, sodium carbonate, borax,potassium carbonate, tripotassium phosphate, potassium bicarbonate, andmixture of the foregoing.
 7. A process according to claim 3, wherein thecorrosion inhibitor is selected from the group consisting of triazoles,benzotriazoles, tetrazoles, imidazoles, benzimidazoles and mixtures ofthe foregoing.
 8. A process according to claim 4, wherein the pre-diphas a pH of from 7 to
 12. 9. A process according to claim, 4, whereinthe pre-dip also comprises a corrosion inhibitor.
 10. A processaccording to claim, 4, wherein the pre-dip comprises a buffer selectedfrom the group consisting of trisodium phosphate, sodium bicarbonate,sodium carbonate, borax, potassium carbonate, potassium bicarbonate,tripotassium phosphate, and mixtures of the foregoing.
 11. A processaccording to claim 4, wherein the adhesion-promoting composition alsocomprises adhesion enhancing species, which species are selected fromthe group consisting of molybdates, tungstates, tantalates, niobates,vanadates, isopoly or heteropoly acids of molybdenum, tungsten,tantalium, niobium, vanadium, and combination of any of the foregoing.12. A process according to claim 8, wherein the pre-dip also comprises acorrosion inhibitor.
 13. A process according to claim 8, wherein thepre-dip comprises a buffer selected from the group consisting oftrisodium phosphate, sodium bicarbonate, sodium carbonate, borax,potassium carbonate, potassium bicarbonate, tripotassium phasphate, andmixtures of the foregoing.
 14. A process according to claim 8, whereinthe adhesion-promoting composition also comprises adhesion enhancingspecies, which species are selected from the group consisting ofmolybdates, tungstates, tantalates, niobates, vanadates, isopoly orheteropoly acids of molybdenum, tungsten, tantalum, niobium, vanadium,and combination of any of the foregoing.
 15. A process according toclaim 9, wherein the pre-dip comprises a buffer selected from the groupconsisting of trisodium phosphate, sodium bicarbonate, sodium carbonate,borax, potassium carbonate, potassium bicarbonate, tripotassiumphosphate, and mixtures of the foregoing.
 16. A process according toclaim 9, wherein the adhesion-promoting composition also comprisesadhesion enhancing species, which species are selected from the groupconsisting of molybdates, tungstates, tantalates, niobates, vanadates,isopoly or heteropoly acids of molybdenum, tungsten, tantalium, niobium,vanadium, and combination of any of the foregoing.
 17. A processaccording to claim 12, wherein the adhesion-promoting composition alsocomprises adhesion enhancing species, which species are selected fromthe group consisting of molybdates, tungstates, tantalates, niobates,vanadates, isopoly or heteropoly acids of molybdenum, tungsten,tantalium, niobium, vanadium, and combinations of any of the foregoing.